Circuit interrupters are electrical components that can be used to break an electrical circuit, interrupting the current flow. A basic example of a circuit interrupter is a switch, which generally consists of two electrical contacts in one of two states; either closed, meaning that the contacts are touching and electricity can flow between them, or open, meaning that the contacts are separated, and no electricity can flow between them. A switch may be directly manipulated by a human to provide a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch.
Another example of a circuit interrupter is a circuit breaker. A circuit breaker may be used, for example, in an electrical panel to limit the electrical current being sent through the electrical wiring. A circuit breaker is designed to protect an electrical circuit from damage caused by an overload or a short circuit. If a fault condition such as a power surge occurs in the electrical wiring, the breaker will trip. This will cause a breaker that was in the “on” position to flip to the “off” position and shut down the electrical power leading from that breaker. When a circuit breaker is tripped, it may prevent a fire from starting on an overloaded circuit; it can also prevent the destruction of the device that is drawing the electricity.
A standard circuit breaker has a terminal connected to a power supply, such as a power line from a power company, and another terminal connected to the circuit that the breaker is intended to protect. Conventionally, these terminals are referred to as the “line” and “load” respectively. The line may sometimes be referred to as the input into the circuit breaker. The load, sometimes referred to as the output, leads out of the circuit breaker and connects to the electrical components being fed from the circuit breaker.
A circuit breaker may be used to protect an individual device, or a number of devices. For example, an individual protected device, such as a single air conditioner, may be directly connected to a circuit breaker. A circuit breaker may also be used to protect multiple devices by connecting to multiple components through a wire which terminates at electrical outlets, for example.
A circuit breaker can be used as a replacement for a fuse. Unlike a fuse however, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Fuses perform much the same circuit protection role as circuit breakers. However circuit breakers may be safer to use in some circumstances than fuses, and may be easier to fix.
In a situation where a fuse blows, interrupting power to a section of a building for example, it may not be apparent which fuse controls the interrupted circuit. In this case, all of the fuses in the electrical panel would need to be inspected to determine which fuse appears burned or spent. This fuse would then need to be removed from the fuse box, and a new fuse would need to be installed.
In this respect, circuit breakers can be much simpler to use than fuses. In a situation where a circuit breaker trips, interrupting power to a section of a building for example, it may be easily apparent which circuit breaker controls the interrupted circuit by looking at the electrical panel and noting which breaker has tripped to the “off” position. This breaker can then be simply flipped to the “on” position and power will resume again.
In general, a typical circuit interrupter has two contacts located inside of a housing. The first contact is stationary, and may be connected to either the line or the load. The second contact is movable with respect to the first contact, such that when the circuit breaker is in the “off” or tripped position, a gap exists between the first and second contact.
A problem with circuit interrupters that operate by separating contacts arises because the energized contacts separate when the circuit breaker is tripped, causing a gap to widen between the contacts while the movable contact moves from a closed position to an open position.
As the contacts begin to separate from the closed position, or approach complete closure from an open position, a very small gap exists between the contacts for a brief time while the contacts are closed or opened. An electric arc may be generated across this gap if the voltage between the contacts is high enough. This is because the breakdown voltage between the contacts is positively related to distance under certain pressure and voltage conditions.
The creation of an arc during switching or tripping the circuit interrupter can result in undesirable side effects which can negatively affect the operation of the circuit interrupter, and which can create a safety hazard.
These effects can have consequences for the operation of the circuit interrupter.
One possible consequence is that the arc may short to other objects in the circuit interrupter and/or to surrounding objects, causing damage and presenting a potential fire or electrocution safety hazard.
Another consequence of arcing is that the arc energy damages the contacts, causing some material to escape into the air as fine particulate matter. The debris which has been melted off of the contacts can migrate or be flung into the mechanism of the circuit interrupter, destroying the mechanism or reducing its operational lifespan.
Another effect of arcing stems from the extremely high temperature of the arc (tens of thousands of degrees Celsius) which can crack the surrounding gas molecules, creating ozone, carbon monoxide, and other compounds. The arc can also ionize the surrounding gasses, potentially creating alternate conduction paths.
Because of these detrimental effects of arcing, it can be very important to quickly cool and quench the arc to prevent damage to the circuit interrupter.
Various techniques for improved arc quenching are known. For example, U.S. Patent Application Publications No. 2012/0037598 and 2012/0261382, assigned to Carling Technologies, Inc., relate to the use of an electromagnetic field to guide the arc toward an arc splitter.
However, generating an electromagnetic field to move the arc consumes power, and generates heat in the device, limiting the applicability of this approach. In addition, the strength of the electromagnetic field depends upon the current flowing through the circuit interrupter, and may not be great enough to sufficiently affect the arc under certain conditions. For example, in some applications a critical current interruption may be required at a low current that would not generate a strong enough electromagnetic field to drive the arc into the arc extinguishing structure, or would require an impractical electromagnet design.
One possible approach to this problem is to incorporate a permanent magnet, which produces a magnetic field without requiring a supply of current. But permanent magnets produce a magnetic field having a fixed direction with respect to the orientation of the magnet, and independent of the current flow through the circuit breaker. Thus, many known solutions for guiding an arc into an arc path using a permanent magnet are dependent on the electrical polarity of the circuit. This is because the direction in which the arc is moved by the fixed magnetic field depends upon the direction the current is flowing through the circuit interrupter.
This can be a significant limitation, because it prevents such devices from being installed in a circuit where the electrical polarity may be reversed. Hazardous conditions may also arise in a situation where such a device is accidentally installed backwards, because the magnetic field ordinarily used to enhance arc quenching will in fact operate to drive the arc away from the arc path. This sensitivity to electrical polarity also precludes permanent magnet solutions from being used in alternating current applications, where the electrical polarity reverses repeatedly.
Recent developments in arc quenching technology have yielded solutions to some of these limitations including an arrangement, which utilizes a permanent magnet that guides the arc toward an arc splitter in a way that is not sensitive to the electrical polarity of the circuit.
However, these arrangements can require the addition of specialized structures into the circuit breaker and may therefore be impractical for certain applications or from the standpoint of design re-use, retrofitting, or upgrade of existing designs. Such arrangements also incorporate a magnetic field having a fixed strength, which does not have the advantage of increasing with current as in electromagnetic designs.
Thus, it is desirable to combine the low current arc arresting of permanent magnet solutions with the electrical polarity independence and increasing field strength of electromagnet solutions.